The present invention relates to methods for making micro-mechanical devices and more particularly to methods for making such devices at the wafer and die level. The invention also relates to forming addressing circuitry and MEMS structures on different wafers, and aligning and bonding the wafers together at the wafer level or die level, with a finer gap adjustment performed at the die level. The invention is also directed to bonding while actuating MEMS structures in real time, or alternating bonding and actuation/measurement steps.
The present application is related to the wafer and die level processes disclosed in U.S. patent application Ser. No. 10/005,308 to Patel et al. filed Dec. 3, 2001 and U.S. patent application Ser. No. 60/276,222 to Patel et al. filed Mar. 15, 2001, each incorporated herein by reference. The present application is also related to micromirror arrays as disclosed in U.S. Pat. Nos. 5,835,256 issued Nov. 10, 1998 and U.S. Pat. No. 6,172,797 issued Jan. 9, 2001, both to Huibers et al. and incorporated herein by reference. Also, as with many MEMS processes, MEMS elements are released towards the end of microfabrication process (but in the present invention, preferably prior to assembly and singulation of the wafer substrates), which release can be performed in accordance with the methods disclosed in U.S. Pat. No. 6,290,865 to Patel et al. issued Sep. 18, 2001, as well as U.S. patent applications Ser. No. 09/649,569 to Patel et al. filed Aug. 28, 2000 and No. 60/298,529 to Reid et al. filed Jun. 15, 2001, each of these being incorporated herein by reference.
The operating (actuation) voltages in a micro-mechanical systems (MEMS) based device can be very sensitive to exact position of the moving components. In one application, an electrostatically actuated micro-mirror array device, mirrors are tilted by applying voltages between a movable electrode attached to the mirror, and a fixed non-movable electrode. If the spacing between these electrodes is non-uniform for different micro-mirrors on the device, the resulting operating voltages can be non-uniform. In addition, the dimensions of the flexing member of a MEMS structure (e.g. the hinge) can change the stiffness of the flexing member, and also can be a large contributor to variation in operating voltages.
It would be desirable to develop a manufacturing process which can reduce variation of operating voltages in MEMS devices, either within a chip or within a group of chips.